The National Fire Protection Association has created a national standard (a code), which is “NFPA 101: Life Safety Code”, that includes requirements for emergency lighting. State and local codes are derived from this standard. NFPA 101 specifies that emergency lighting provide enough illumination throughout the building so that the occupants can safely exit the building in the event of failure of normal power. The failures specified in section 7.9.2.3 of NFPA 101 are:                Failure of a public utility or other outside electrical power supply,        Opening of a circuit breaker or fuse,        Manual acts, including accidentally opening of a switch controlling normal lighting facilities.        
Emergency lighting can be energized by emergency power or by a battery per emergency light fixture. There are tradeoffs as to which approach is used. These are primarily installation and component costs, ongoing maintenance costs, aesthetics, and compatibility with use.
A first implementation of emergency lighting includes a dedicated emergency light fixture connected to a circuit that supplies only “emergency power”.
A second implementation of emergency lighting includes a dedicated emergency light fixture connected to a circuit that supplies only “normal power” when it is available, and “emergency power” when normal power fails. The circuit must contain a UL 1008 automatic transfer switch (ATS) that switches between the normal power and the emergency power feeds. The downside to this approach is that the light is continuously on, and a special circuit must be provisioned.
A third implementation includes a dual purpose light fixture that functions as a normal light and is controlled with an on/off switch when normal power is present and functions as an emergency light when emergency power is present (the setting of the on/off switch is ignored). This is similar to a dedicated fixture, in that it has a circuit that supplies “normal power” or “emergency power”, but in addition, it has a UL 924 bypass (or shunt) switch so that when “normal power” is supplied, the light is user controllable with the on/off switch, and the on/off switch is bypassed (ignored) when “emergency power” is supplied. The cost of this approach is higher than the second implementation, due to the additional circuit and an UL 924 switch.
It is desirable to have a lighting method, system and apparatus for providing emergency lighting that also provides power conservation.